Rheostat



F. G. LOGAN RHEOSTAT INVENTOR 2 Sheets-Sheet l 6 PA/Y/r 6 [066 BY M ATTORN Original Filed Jan. 18, 1939 Dec. 16, 1941. F G, LOGAN 2,266,222

RHEOSTAT Original Filed Jan. 18, 1939 2 Sheets-Sheet 2 INVENTOR Emu #6: [0619 ATTORNEY Patented Dec. 16, 1941 UNITED STATES PATENT OFFICE 2,266,222 RHEOSTAT Frank G. Logan, Ward Leonard of New York Original application 251,468. Divided Mount Vernon, N. Y., assignor to Electric Company, acorporation January 18, 1939, Serial No. and this application December 9, 1939, Serial No. 308,341

' and 8 are similar views showing a form of re- 8 Claims.

justments.

This application is application Serial No. 1939.

The main objects of the invention are to provide a simple and inexpensive form of construction which will be dependable in operation, rugged and compact in structure, not easily affected by tilt or shock and adapted to witha division of my pending 251,468, filed January 18,

stand severe service with a minimum amount of attention. Another object is to provide means whereby the resistance maybe adjusted within comparatively close limits and wherein a proresistance may be quickly obtained by a comparatively small movement of the movable element. Another object is to pro-- which the movable parts will have comparatively a small mass and inertia. Another object is to provide a wiping contact between the movable element and the resistance sparking. Another object is to provide a form of relative movement between the resistance contacts and the movable element which will be along the contacts instead of across them which reduces the friction and wear of the parts and heightens the smoothness of control. Other objects and advantages of the invention will be understood from the following description and accompanying drawings showing preferred embodiments of the invention.

Fig. 1 is a front elevation of the controlling device and adjustable resistance of the regulator; Fig. 2 is a side view partly in section; Figs. 3, 4 and 5 are front plan and side views showing a difierent form of resistance unit; Fig. 6 is a -iront view of the movable contact and resistance element showing a diilerent form; and Figs. 7

sistance and contacts adapted I01 heavy duty.

l. 'ihe regulating the Iorm or a tube extending horizontally across the top portion or the casing. it is composed of a tune za 0i insulating rerractory material, such as porcelain, on which are wound many turns 01' the resistive conductor zb connected to terminals 20 at the ends of the tube. The

for the purpose of securing desired control.

Below the resistance unit is mounted the controlling electro-magnet or solenoid having a vertical coil 4 with and the supslotted as shown of which contacts with the exposed portions of the turns of the resistance unit. It is of a widely open V form with the ends 8a extending upward vertically. It is preferably made of silver, or alloy of silver for insuring good contact with the turns of the resistive conductor but may, if desired, be made of a baser metal with the contacting portion of silver or of silver alloy. At the central apex of the contacting element 8 are secured .brackets 9 which engage the opposite sides of a connecting strip iii of insulat ing material. This strip extends downwardly into the coil 4 and is pivotally connected to the upper end of the plunger 1. The plunger 8 may be slotted longitudinally from the center outwardly as shown at la for reducing the induction of eddy currents. The proper contact pressure of the movable element 8 against the contact edge of the resistance tube is imposed by a spring ii secured at one end to theupper part of the strip it and at the other end to the end of a screw H which is fixed toand projects forwardly from the back of the casing. This insures that an equal pressure will be imposed on each leg of the V against the contacts and likewise insures that the contact pressure will be substantially uniform in all positions of the parts. A spring i3 is secured to the lower end of the plunger 1 and to a sheet metal plate l4 which is fixedto the back ofthe casing. This spring exerts a downward pull upon the plunger I and supplements the force of gravity tending to hold the same in its lowest position. At the lower end of the plunger is secured a small plate 15 which projects towards the back of the casing into a cutaway portion I la of the plate M. The plate thus serves as a stop for the plunger in its lowest and highest positions.

When the plunger is in its lowest position as shown in Figs. 1 and 2, the outer ends of the contacting element 8 are in engagement with the exposed portiions of the terminal bands 20 and thereby short circuits all of the resistance or the tube 2. When the current in the coil 4 is increased, the plunger 1 is raised against gravity and the pull of the spring l8 and this action gradually reduces the short circuited portion of the resistive conductor; and when the plunger is in its highest position with the plate l5 against the upper stop, the middle of the element 8 is in engagement with the middle of the resistive conductor, at which time almost none of the resistance is short circuited by the element 8 and it is practically all inserted in the circuit to which the resistive conductor is connected. By this form of construction the distance of travel of the plunger and contacting element 8 is comparatively short by reason of the wide open V form of the movable element. This small range of movement from the resistance-all-out positionto the resistanceall-in position insures a pronounced change of resistance with a comparatively small movement of the plunger and consequently imposes an adequate corrective change of resistance upon comparatively small change of current in the solenoid coil. Also, the multiplicity of contacts of the exposed portion of the resistive conductor secures refined control of the resistance upon any movement of the contacting element. The direction of movement of the element 8 over the exposed surface of the resistive conductor is always in the direction of the turns of the resistive conductor and not across them, securing a wiping contact with a minimum of frictional wear, while the spring ll insure adequate and uniform con- 7 tact pressure in all positions of the controlling element. Furthermore, the weight of the movable parts is comparatively light permitting quick response of movement to any change of current and the low inertia likewise permits the movable portion of the system to quickly adjust itself to its correct position under any conditions of operation.

The form of construction may be changed to suit particular requirements and Figs. 3 to 8 show some of the modified forms which may be used for special purposes. Figs. 3 to 5 show a form of contact resistance element similar to that shown in Figs. 1 and 2 except that the resistive conductor is wound in the form of a flat plate 18 having a front contacting straight edge Na where portions of the successive turns of the resistive conductor are exposed for engagement by the movable element 83. As shown in Fig. 4 the rearwardly extending portion of the plate may be ,made converging to permit the same size of resistive conductor to be used throughout its length, the shorter length of the turns at the ends securing a less change of resistance per turn near the end portion'than is secured at the central portion of the plate.

Fig. 6 shows the shape of the parts reversed from that of Figs. 1 and 2. In Fig. 6 the movable contact element i1 is in the form of a straight strip or bar whereas the exposed contacting face E8 of the successive turns of the resistive conductor is of an inverted V-shape with widely diverging sides. Such a form of resistance element may be made by combining two flat plates meeting at the apex as shown in Fig. 6, or by similarly combining other forms of resistance units such as the tubular form of Figs. 1 and 2. Fig. 7 indicates a form particularly appropriate for use where the control of comparatively large current tacts i9 with resistive conductors 20 connected between successive'contacts, the resistive wires being preferably covered with an insulating coating from which the contacts I! project, as in the usual forms of plate rheostats. Fig. 8 is similar to Fig. 7 except that the movable contacting element i1 is in the form of a straight bar or strip, while the contacts l8 are arranged to form an inverted widely diverging V. It is evident that in each of these modifications the resistance is all short circuited when the movable contacting bar or strip is in its lowestposition and is all inserted when in its upper position.

Instead of making the contacting bar or the contacts of wide open V formation, they could be arc shaped or of bow form or of any other equivalent form to secure the same results; and the description as of V form and the direction of the two legs of the V forming an obtuse angle between the legs in the claims is .to be understood as covering such equivalents.

The invention is applicable to various uses and for various purposes, particularly where a large range of control and refined adjustment is desired to be accomplished by a comparatively short range of movement of the adjustable element. Various modifications may be made according to the conditions and particular requirements without departing from the scope of the invention.

I claim:

1. A rheostat comprising a resistive device having a plurality of contact surfaces adjoining each other in a row to form a contact member, an element contacting therewith to form a second 5 contact member, one of said members extending is necessary. Here there is a straight row or conin an approximately straight line and the other of said members having a wide open V contact form and the direction of the two legs of the dicular to said line and the contact. engagement in the direction of relative movement being small.

2'. A rheostat comprising a resistive device having. a plurality of contact surfaces adjoining each other in a row to form a contact member, the contact surfaces thereof being in the form of a narrow projecting edge to have small contacting surfaces, an element contacting therewith to form a second turns of a resistive conductor thereon, said conductor having a narrow row of exposed contact contact member, one of surfaces adjoining each other to form a contact I member, an element contacting therewithto 4. A rheostat, comprising a support having turns of a resistive conductor thereon, said conductor having a narrow row of exposed contact surfaces adjoining each other to form a contact member, an element contacting therewith to form a second contact member, one of said members wide open V the two legs .of the V forming an obtuse angle between the legs and contacting with the other member at each leg of the V, and means for movhaving a plurality of fixed contact surfaces adjoining each other in a row to form a contact member, a movable element contacting therewith to form a second contact member, one of said members extending in an approximately straight line and the other of said members hav ing a wide open V contact form and the direction of the two legs of the V forming an obtuse angle between the legs and contacting with the other member ment against said fixed contacts with the same pressure at eac leg of the V.

8. A rheostat comprising a resistive device haying a plurality of fixed contact surfaces adjoining each other in a narrow row and extending in the direction of the obtuse angle between the with said'surfaces at each legs and contacting leg of the V, a sole noid for moving said element in a direction perpendicular to said line. and means for pressing said movable element against said contact surfaces with the same pressure at each leg of the V.

FRANK G. IDGAN.

an approximately straight line, a movable I 7 element having a wide open V contact form and 

